It's pretty clear how it's gonna work for say DG, but I'm especially curious regarding Wild Imps considering the current tooltip states 10 bolts instead of a duration.

Edit (source) :

The following summoned pets/totems will now chain cast their spells with no delay between casts, allowing them to cast their spells more frequently in the same amount of time.
Death Knight: Gargoyle
Druid: Force of Nature (Balance, Restoration), Mirror Image (Symbiosis)
Mage: Mirror Image, Water Elemental
Shaman: Searing Totem
Warlock: Doomguard, Terrorguard, Wild Imp

It's pretty clear how it's gonna work for say DG, but I'm especially curious regarding Wild Imps considering the current tooltip states 10 bolts instead of a duration.

Guardians have scaled with haste since 5.0. The change has nothing to do with haste, but it means they now chain cast their abilities rather than sitting there idling between casts. Summon a Doomguard/Terrorguard while attacking a target dummy and set focus to it, watch as it casts Doombolt, then sits there for 1/2 a second not doing anything, then casts another, then sits there for 1/2 a second, etc etc. Same story with Wild Imps. Just QoL fixes that should give a little bit of a burst DPS increase, and a (very) minor DPS boost overall.

Regarding that, has anyone tested or mathed out if that will be a dps increase in any way? And if so, how much? I realize it says the same amount of spells for wild imps, but what about the doom/terrorguard?

With doomguard you may squeeze up to ~500k dmg over a whole fight with the change, Wild Imps is such a big chunck of your damage right now that it would be a significant buff to have them somehow scale with haste (of course if it's only firing the 10 bolts quicker, that's not much of a benefit !).

Zumzum, isn't the scaling with Haste for Pets and Guardians nothing more than cast speed (or melee swing speed), and Fel Energy regeneration rate? I was under the impression that the Doomguard already scaled with haste. Or is it currently bugged and the Fel Energy regen rate is unaffected? Haven't really looked it that much, just assumed it was as it should be.

Surutcra, I doubt it'd be a 500k damage thing, due to limitations with Fel Energy. As it is my Doomguard only does around 1.0M damage (at least this is what I'm seeing relatively consistently with my own, at my current gear level.) It might be about 150k, give or take, plus or minus whatever damage modifiers are applicable on the fight, but it can only cast so many Doom bolts with a 35 Fel Energy cost. The difference is that now, rather than pooling Fel Energy, it'll be Fel Energy starved instead, meaning it's at least pumping out every single Doom Bolt it possibly can, but I can only see an extra 100-200k damage from that, at MOST.

Wild Imps won't be gaining any extra bolts. It's exactly as you just said. They now fire out their 10 bolts quicker and despawn. It's just a small burst DPS increase. Nothing more. Useful for PvP, not so useful for PvE. It might increase your overall DPS a little if the boss has debuff on it that increases damage taken for a short time, and the wild imps cast more bolts (than they currently would've) in that window with the increased damage modifier, but that likely won't be anything significant. (Think Tortos with Shell Concussion. Say a wild imp spawns with 10s left on the debuff, it casts 3 bolts in that 10s window that hit the boss 25% harder, then 7 bolts that just hit the boss normally. Now, instead, it could cast 5 bolts that hit 25% harder, then 5 that hit normally. Very marginal overall DPS increase.) (Purely theoretical numbers)